In order to promote safe running of a vehicle it is essential to maintain the vehicle wheels in a normal state. For example, if the vehicle is run for a long period while the tires have low pressure or high temperature, tire reliability is impaired. This fall in reliability can cause, in certain circumstances, various undesirable phenomenon. To address this problem, technology is required that suitably monitors various states of each wheel, such as the air pressure and temperature of the tire, and warns the driver at an early stage when an abnormality is detected.
Japanese Utility Model Publication No. JP U H5-13802 discloses a tire air pressure warning system including: a vehicle wheel communication device which is provided at a vehicle wheel and which transmits tire air pressure information; and a vehicle body receiver which is provided at a vehicle body and which receives the tire air pressure information from the vehicle wheel communication device.
However, a prerequisite of the tire air pressure warning system of Japanese Utility Model Publication JP U H5-13802 is that a single vehicle wheel communication device is provided in each of the vehicle wheels. As a result, in the case that a plurality of vehicle wheel communication devices are provided in each vehicle wheel, signal interference problems occur. In order to ascertain the state of each vehicle wheel, various types of sensor information related to air pressure, temperature, and the like, are required as vehicle wheel information. Moreover, when temperature is detected, for example, sensor information from different positions or parts, such as the tire and wheel, are necessary. Accordingly, there is a need for a technology that includes a plurality of sensors on each vehicle wheel and a plurality of communication devices for receiving and transmitting respective outputs of the sensors, in which signals transmitted from the plurality of vehicle wheel communication devices are able to be received and processed without interference.
Further, with the tire air pressure warning system of Japanese Utility Model Publication JP U H5-13802, signal transmission by the vehicle wheel communication device is performed using a different prime number cycle for each vehicle wheel. However, with this method, if the number of vehicle wheel communication devices are increased, the transmission cycle becomes longer, which causes variation in the amount of information that can be obtained.